There are substantial deposits of oil sands in the world with particularly large deposits in Canada and Venezuela. For example, the Athabasca oil sands region of the Western Canadian Sedimentary Basin contains an estimated 1.3 trillion bbls of potentially recoverable bitumen. There are lesser, but significant deposits, found in the U.S. and other countries. These oil sands contain a petroleum substance called bitumen or heavy oil. Oil Sands deposits cannot be economically exploited by traditional oil well technology because the bitumen or heavy oil is too viscous to flow at natural reservoir temperatures.
When oil sand deposits are near the surface, they can be economically recovered by surface mining methods. The bitumen is then retrieved by an the extraction process and finally taken to an upgrader facility where it is refined and converted into crude oil and other petroleum products.
The Canadian oil sands surface mining community is evaluating advanced surface mining machines that can excavate material at an open face and process the excavated oil sands directly into a dirty bitumen froth. If such machines are successful, they could replace the shovels and trucks, slurry conversion facility, long hydrotransport haulage and primary bitumen extraction facilities that are currently used.
When oil sand deposits are too far below the surface for economic recovery by surface mining, bitumen can be economically recovered in many but not all areas by recently developed in-situ recovery methods such as SAGD (Steam Assisted Gravity Drain) or other variants of gravity drain technology which can mobilize the bitumen or heavy oil.
Roughly 65% or approximately 800 billion barrels of the bitumen in the Athabasca cannot be recovered by either surface mining or in-situ technologies. A large fraction of these currently inaccessible deposits are too deep for recovery by any known technology. However, there is a considerable portion that are in relatively shallow deposits where either (1) the overburden is too thick and/or there is too much water-laden muskeg for economical recovery by surface mining operations; (2) the oil sands deposits are too shallow for SAGD and other thermal in-situ recovery processes to be applied effectively; or (3) the oil sands deposits are too thin (typically less than 20 meters thick) for use efficient use of either surface mining or in-situ methods. Estimates for economical grade bitumen in these areas range from 30 to 100 billion barrels.
Some of these deposits may be exploited by an appropriate underground mining technology. Although intensely studied in the 1970s and early 1980s, no economically viable underground mining concept has ever been developed for the oil sands. In 2001, an underground mining method was proposed based on the use of large, soft-ground tunneling machines designed to backfill most of the tailings behind the advancing machine. A description of this concept is included in U.S. Pat. No. 6,554,368 “Method And System for Mining Hydrocarbon-Containing Materials” which is incorporated herein by reference. One embodiment of the mining method envisioned by U.S. Pat. No. 6,554,368 involves the combination of slurry TBM or other fully shielded mining machine excavation techniques with hydrotransport haulage systems as developed by the oil sands surface mining industry. In another embodiment, the bitumen may be separated inside the TBM or mining machine by any number of various extraction technologies.
In mining operations where an oil sands ore is produced, there are several bitumen extraction processes that are either in current use or under consideration.
These include the Clark hot water process which is discussed in a paper “Athabasca Mineable Oil Sands: The RTR/Gulf Extraction Process—Theoretical Model of Detachment” by Corti and Dente which is incorporated herein by reference. The Clark process has disadvantages, some of which are discussed in the introductory passage of U.S. Pat. No. 4,946,597 which is incorporated herein by reference, notably a requirement for a large net input of thermal and mechanical energy, complex procedures for separating the released oil, and the generation of large quantities of sludge requiring indefinite storage.
The Corti and Dente paper suggests that better results should be obtained with a proper balance of mechanical action and heat application. Canadian Patent 1,165,712 which is incorporated herein by reference, points out that more moderate mechanical action will reduce disaggregation of the clay content of the sands. Separator cells, ablation drums, and huge inter-stage tanks are typical of apparatuses necessary in oil sands extraction. An example of one of these is the Bitmin drum or counter-current desander CCDS. Canadian Patent 2,124,199 “Method and Apparatus for Releasing and Separating Oil from Oil Sands” describes a process for separating bitumen from its sand matrix form and feedstock of oil sands.
Another oil sands extraction method is based on cyclo-separators (also known as hydrocyclones) in which centrifugal action is used to separate the low specific gravity materials (bitumen and water) from the higher specific gravity materials (sand, clays etc).
Canadian Patent 2,332,207 describes a surface mining process carried in a mobile facility which consists of a surface mining apparatus on which is mounted an extraction facility comprised of one or more hydrocyclones and associated equipment. The oil sands material is excavated by one or more cutting heads, sent through a crusher to remove oversized ore lumps and then mixed with a suitable solvent such as water in a slurry mixing tank. The slurry is fed into one or more hydrocylcones. Each hydrocyclone typically separates about 70% of the bitumen from the input feed. Thus a bank of three hydrocylcones can be expected to separate as much as 95% of the bitumen from the original ore. The product of this process is a dirty bitumen stream that is ready for a froth treatment plant. The waste from this process is a tailings stream which is typically less than 15% by mass water. The de-watered waste produced by this process may be deposited directly on the excavated surface without need for large tailings ponds, characteristic of current surface mining practice.
In a mining recovery operation, the most efficient way to process oil sands is to excavate and process the ore as close to the excavation face as possible. If this can be done using an underground mining technique, then the requirement to remove large tracts of overburden is eliminated. Further, the tailings can be placed directly back in the ground thereby substantially reducing a tailings disposal problem. The extraction process for removing the bitumen from the ore requires substantial energy. If a large portion of this energy can be utilized from the waste heat of the excavation process, then this results in less overall greenhouse emissions. In addition, if the ore is processed underground, methane liberated in the process can also be captured and not released as a greenhouse gas.
There is thus a need for a bitumen/heavy oil recovery method in oil sands that can be used to:
a) extend mining underground to substantially eliminate overburden removal costs;
b) avoid the relatively uncontrollable separation of bitumen in hydrotransport systems;
c) properly condition the oil sands for further processing underground, including crushing;
d) separate most of the bitumen from the sands underground inside the excavating machine;
e) produce a bitumen slurry underground for hydrotransport to the surface;
f) prepare waste material for direct backfill behind the mining machine so as to reduce the haulage of material and minimize the management of tailings and other waste materials;
g) reduce the output of carbon dioxide and methane emissions released by the recovery of bitumen from the oil sands; and
h) utilize as many of the existing and proven engineering and technical advances of the mining and civil excavation industries as possible.